Effect of heat treatment on tensile properties of friction stir welded joints of 2219-T6 aluminium alloy

Abstract

The effect of post-weld heat treatment (PWHT) on the tensile properties of friction stir welded (FSW) joints of 2219-T6 aluminium alloy was investigated. The PWHT was carried out at aging temperature of 165°C for 18 h. The mechanical properties of the joints were evaluated using tensile tests. The experimental results indicate that the PWHT significantly influences the tensile properties of the FSW joints. After the heat treatment, the tensile strength of the joints increases and the elongation at fracture of the joints decreases. The maximum tensile strength of the joints is equivalent to 89% of that of the base material. The fracture location characteristics of the heat treated joints are similar to those of the as welded joints. The defect free joints fracture in the heat affected zone on the retreating side and the joints with a void defect fracture in the weld zone on the advancing side. All of the experimental results can be explained by the hardness profiles and welding defects in the joints.     

Effect of post weld heat treatment on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel weldments

The effect of postweld heat treatment (PWHT) on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel joints with ER316LMn filler material was investigated. PWHT aging was performed for 1 h at four different temperatures of 600 °C, 760 °C, 870 °C and 920 °C, respectively. The microstructure revealed the sigma phase precipitation occurred in the weld metals heat-treated at the temperature of 870 °C and 920 °C. The PWHT temperatures have the less effect on the tensile strength, and the maximum tensile strength of the joints is about 630 MPa, reaching the 95% of the base metal, whereas the elongation is enhanced with the rise of PWHT temperatures. Meanwhile, the sigma phase precipitation in the weld metals reduces the impact toughness.     

Effect of temperature on the fracture behaviour of heat‐treated Al–Cu–Li alloy laser welds under low‐cycle fatigue loading

The paper presents the results of the studies of the effect of temperature on the fracture behaviour of Al–Cu–Li alloy laser welds under low‐cycle fatigue loading. The mechanical properties and the microstructure of the welded joints without and after postweld heat treatment (PWHT) were investigated. The tensile strength and the low‐cycle fatigue resistance of the welded joints were studied at various test temperatures (20°C, 85°C and ? 60°C). It was been found that heating up to 85°C and cooling down to ?60°C reduced the maximum number of loading cycles of the welded joints after PWHT by 1.5–2.0 times compared with that at a test temperature of 20°C.     

Influence of postweld heat treatment on creep properties of 1CrO.5Mo and 2.25Cr1Mo weldments

The creep properties of simulated heat-affected zone, weld metal and cross-weld specimens of tCr0.5Mo and cross-weld specimens of 2.25Cr tMo have been studied with reference to the effect of postweld heat treatment (PWHT). A reduction in the creep rupture strength of up to 20% has been observed after PWHT. Contrary to what has been previously proposed, PWHT was in the present investigation found to have only a marginal influence on the creep ductility. The creep rate can increase by up to a factor of 2-4 after postweld heat treatment, probably because of-carbide coarsening during the heat treatment. Preheating at 200°C did not affect the creep properties of 2.25Cr lMo. Overheating, on the other hand, at 650°C for 1000h reduced the rupture time of tCr0.5Mo by almost an order of magnitude. The tensile strength and yield strength of tCrO.5Mo were significantly reduced after postweld heat treatment. Reductions of up to 100-200MPa were observed both at room temperature and at 550°C in some cases.     

5083铝合金搅拌摩擦焊接头拉伸行为研究

目的 研究5083铝合金搅拌摩擦焊接（FSW）的组织、力学性能和拉伸应变,分析接头的拉伸行为。方法 采用数码相机、光学显微镜、电子扫描显微镜等表征分析方法,对焊缝的表面宏观成形、微观组织、断口形貌进行分析;利用拉伸机、三维数字动态散斑应变测量分析系统和显微维氏硬度计对接头的力学性能和拉伸应变进行测试。结果 不同焊接工艺参数下FSW接头的最低抗拉强度为305 MPa,断后延伸率达到了14%以上;焊核区拉伸应变沿板厚方向呈现上高下低和上宽下窄的不均匀梯度分布,发生了较大程度的变形强化,直到拉伸应力达到抗拉强度。断裂失效前300/120接头的最大拉伸应变在晶粒粗大的母材区,500/120和500/200接头的最大拉伸应变则位于晶粒尺寸差异较大的后退侧焊核区与热力影响区交界处。接头拉伸断口宏观上均为45°剪切韧性断裂,微观上均以韧窝韧性断裂为主,而高热输入500/120接头出现脆性断裂特征,其延伸率明显降低。结论 高热力耦合输入使铝合金FSW接头薄弱区发生转变,强韧性降低。     

Study of microstructural and mechanical properties of weld heat affected zones of 2024-T3 aluminium using Gleeble simulation

Abstract

The effect of the microstructural properties on the mechanical properties of welding thermal cycles and post-weld heat treatment of the heat affected zone (HAZ) in 2024-T3 aluminium alloy has been investigated. Gleeble HAZ simulation, differential scanning calorimetry, TEM and tensile test have been utilised to investigate the regions representative of HAZ microstructures. The decay of strength in the weld HAZ is primarily due to the precipitation and coarsening of stable S phases. The welded HAZ in the region at peak temperature of 414°C has the lowest strength after natural aged temper. Post-weld T81 artificial aging (PWAA-T81) heat treatment at 190°C for 12 h has no effect on improving the HAZ strength; the HAZ strength of 2024-T3 alloy obtained by PWAA-T81 treatment is less than that obtained by natural aging, and its lowest strength is shifted to the region of the peak temperature, which is 452°C. Scanning electron microscopy observation reveals that the fracture mode changes from transgranular to intergranular failure when the 2024 specimen is exposed to a thermal cycle up to a peak temperature of 550°C. This is caused by the liquation of grain boundary segregates or formation of a eutectic structure while the specimen is subjected to high temperature thermal cycles during welding, which results in a decrease in the strength and ductility of the grain boundary. It is also shown that the decrease in ductility in this high temperature HAZ cannot be improved using the PWAA-T81 heat treatment.     

Effect of post-weld heat treatment and electrolytic plasma processing on tungsten inert gas welded AISI 4140 alloy steel

Post-weld heat treatment (PWHT) is commonly adopted on welded joints and structures to relieve post-weld residual stresses; and restore the mechanical properties and structural integrity. An electrolytic plasma process (EPP) has been developed to improve corrosion behavior and wear resistance of structural materials; and can be employed in other applications and surface modifications aspects. In this study the effects of PWHT and EPP on the residual stresses, micro-hardness, microstructures, and uniaxial tensile properties are explored on tungsten inert gas (TIG) welded AISI-4140 alloys steel with SAE-4130 chromium–molybdenum alloy welding filler rod. For rational comparison all of the welded samples are checked with nondestructive Phased Array Ultrasonic Testing (PAUT) and to ensure defect-free samples before testing. Residual stresses are assessed with ultrasonic testing at different distances from weld center line. PWHT resulted in relief of tensile residual stress due to grain refinement. As a consequence higher ductility but lower strength existed in PWHT samples. In comparison, EPP-treated samples revealed lower residual stresses, but no significant variation on the grain refinement. Consequently, EPP-treated specimens exhibited higher tensile strength but lower ductility and toughness for the martensitic formation due to the rapid heating and quenching effects. EPP was also applied on PWHT samples, but which did not reveal any substantial effect on the tensile properties after PWHT at 650 °C. Finally the microstructures and fracture morphology are analyzed using scanning electron microscopy (SEM) and optical microscope to study the evolution of microstructures.     

Improving tensile strength and bend ductility of titanium/AlSI 304L stainless steel friction welds

Abstract

The metallurgical and mechanical properties of friction welds between titanium and AISI 304L stainless steel were examined. Joint tensile strength increased when high friction pressure (>196 MN m^?2) and high upsetting pressure (294 MN m^?2) were used during welding. Although the surface roughness of the titanium substrate had no effect on joint strength, decreasing the surface roughness of the AISI 304L material did increase the tensile strength of completed joints. As welded dissimilar joints had poor bend test ductility and failed in the interface region. Detailed microscopy and X-ray diffraction analysis confirmed that the poor bend ductility was caused by a combination of high hardness of the titanium material immediately adjacent to the joint interface, the presence of unrelieved residual strain at the joint interface, and intermetallic phases formed during the welding operation. Detailed transmission electron microscopy and X-ray analysis confirmed that a thin layer rich in intermetallics was present in the as welded joints. (FeNiCr)Ti phases were formed during seizure formation and disruption; this provided the necessary conditions for anomalously high rates of diffusion of titanium in stainless steel, and of iron, chromium, and nickel in titanium. Low temperature post-weld heat treatment (PWHT), involving heating to 500–600°C followed by immediate air cooling, reduced intermetallic precipitation, promoted stress relaxation, and facilitated complete bonding across the whole joint interface. This treatment markedly improved bend ductility and had a negligible effect on joint tensile strength. High PWHT temperatures (≥900°C) and long holding times at temperature markedly reduced joint tensile strength and bend ductility, owing to excessive formation of intermetallic phases at the joint interface.

MST/1521     

Improved properties of friction stir-welded AZ31 magnesium alloy by post-weld heat treatment

Mechanical properties and microstructure of friction stir-welded AZ31 based on variety post-weld heat treatment (PWHT) temperatures were evaluated, and an optimal PWHT condition was identified. At rotational speed of 1200?rev?min^?1 and welding speed of 300?mm?min^?1, the average yield tensile, tensile strength and elongation of friction stir-welded joints was 92.5?MPa, 199.1?MPa and 7.3%, respectively. It was found that (300°C – 1?h) heat treatment after welding was more beneficial than other heat treatments in enhancing the mechanical properties and homogenising grain size. The maximum yield and tensile strength was 139.9 and 238.4?MPa, respectively, tensile longitudinal and compressive transverse residual stress could be effectively eliminated, and the fatigue strength increased 34.2% comparing with as-welded joints.     

The effect of post-weld heat treatment on the mechanical properties of 2024-T4 friction stir-welded joints

In this study, the effect of post-weld heat treatment (PWHT) on the mechanical properties of friction stir-welded 2024 aluminum alloys in the T4 temper state was investigated. Solution heat treatment and various ageing treatments were given to the welded joints. The PWHT procedures caused abnormal coarsening of the grains in the weld zone, which resulted in a drop in micro-hardness at the weld zone compared to the base material of the joints. T6 (190 °C – 10 h) ageing treatment after welding was found to be more beneficial than the other heat treatments in enhancing the mechanical properties of the 2024-T4 joints. However, the T6 (190 °C – 10 h) heat treatment led to significant ductility deterioration in the joint.     

Correlation of microstructure with mechanical properties of TIG weldments of Ti–6Al–4V made with and without current pulsing

This paper deals with the influence of direct current pulsing on the microstructure, room temperature hardness and tensile properties at four different temperatures of tungsten inert gas (TIG) weldments of Ti–6Al–4V. Autogenous full-penetration bead-on-plate TIG welds were made with and without direct current pulsing. A few coupons were subjected to a post-weld heat treatment (PWHT) at 900 °C. Room temperature hardness and tensile properties at four different temperatures (25, 150, 300 and 450 °C) of the weldments in both as-welded and PWHT conditions were studied and correlated with the microstructure. Current pulsing resulted in slight refinement of prior β grains leading to higher hardness, tensile strength and ductility of weldments in the as-welded condition. The post-weld heat treatment at 900 °C resulted in improvement in ductility and reduction in strength of weldments (both unpulsed and pulsed) owing to more coarsening of α, reduction in defect density and decomposition of martensite to equilibrium α and β. Both pulsed and unpulsed weldments after PWHT exhibited almost the same values of strength and ductility. This may be attributed to the width of the α plates being almost the same in both welds.     

High temperature tensile properties of oxide dispersion strengthened T91 and their correlation with microstructural evolution

Abstract

In the present work, high temperature deformation behavior of oxide dispersion strengthened T91 was investigated and linked to the corresponding microstructure. First, tensile properties are presented and discussed in terms of yield strength, tensile stress and total elongation as a function of temperature. The results are compared to the matrix material and other ODS alloys. Second, transmission electron microscopy was applied to as received and deformed tensile test specimens. It is shown that the Y₂O₃ particle diameter increases slightly upon deformation at elevated temperatures. Additionally, distinctive coarsening of M₂₃C₆ carbides occurs at prior austenite grain boundaries. At temperatures above 500°C, dislocations are straight and pile up at grain boundaries due to thermally activated climbing. Oxide dispersion strengthened T91 provides high strength due to strong particle/dislocation interactions and good toughness properties.     

Effect of heat input on the microstructure and mechanical properties of gas tungsten arc welded AISI 304 stainless steel joints

Influence of heat input on the microstructure and mechanical properties of gas tungsten arc welded 304 stainless steel (SS) joints was studied. Three heat input combinations designated as low heat (2.563 kJ/mm), medium heat (2.784 kJ/mm) and high heat (3.017 kJ/mm) were selected from the operating window of the gas tungsten arc welding process (GTAW) and weld joints made using these combinations were subjected to microstructural evaluations and tensile testing so as to analyze the effect of thermal arc energy on the microstructure and mechanical properties of these joints. The results of this investigation indicate that the joints made using low heat input exhibited higher ultimate tensile strength (UTS) than those welded with medium and high heat input. Significant grain coarsening was observed in the heat affected zone (HAZ) of all the joints and it was found that the extent of grain coarsening in the heat affected zone increased with increase in the heat input. For the joints investigated in this study it was also found that average dendrite length and inter-dendritic spacing in the weld zone increases with increase in the heat input which is the main reason for the observable changes in the tensile properties of the weld joints welded with different arc energy inputs.     

The effect of post weld heat treatment on the properties of 6061 friction stir welded joints

Post weld heat treatment (PWHT) of Friction Stir Welds (FSW) was carried out at solutioninsing temperatures of 520, 540, and 560°C followed by ageing at 175°C or 200°C. It was found that the weld (stir) region exhibited very coarse grains after the PWHT. The hardness was found to be uniform across the weldment after the PWHT. The samples failed after PWHT during root bend test. Heat treatments to reduce the grain size did not reduce the brittleness of the welds. The brittleness was attributed to the presence of precipitate free zones adjacent to the grain boundaries and the equiaxed structure of the weldment microstructure and the failure was due to a ductile intergranular fracture mechanism.     

Effect of microstructure and low cycle fatigue deformation on tensile properties of P91 steel

Isothermal furnace heat treatments were carried out to simulate the microstructures of inter-critical, fine grain and coarse grain heat-affected zones of P91 steel weld joint at different soaking temperatures ranging from just above AC₁ (837 °C) to well above AC₃ (903 °C). Interrupted low cycle fatigue tests were performed on the specimens of P91 steel up to 5 %, 10 %, 30 %, and 50 % of the total fatigue life at the strain amplitude of ±0.6 %, strain rate of 0.003 s⁻¹ and temperatures of 550 °C and 600 °C. Subsequently, tensile tests were conducted on the interrupt tested specimens at the same strain rate and temperatures. Soaking at the inter-critical temperature region reduces / deteriorates the tensile and yield strengths of base metal compared to fine grain and coarse grain regions. The inter-critical heat-affected zone accounted higher damage contribution towards the overall tensile behavior of the actual P91 steel weld joint. Substructural coarsening during strain cycling at elevated temperatures attributes to the rapid reduction in the initial yield strength up to 10 % of fatigue life of P91 steel. A higher amount of plastic strain accumulation during low cycle fatigue deformation resulted in a decrease in fatigue life of the inter-critical heat-affected zone of P91 steel.     

Evolution of grain structure across joints in friction stir welded EN AW 5083 H111 plates during thermal exposure

Abstract

The mechanisms involved in the coarsening of the grain structure across FSW joints produced in EN AW 5083 H111 plates with different pin profiles were investigated. The grain coarsening across the FSW joints invariably starts inside the shoulder flow zones and involves both abnormal growth of the grains inside the dynamically recrystallised regions as well as recrystallisation of the deformed grains outside these regions. The elliptical nugget zones produced with the threaded circular pins appear to be more stable with respect to the basin shaped counterparts obtained with the triangular pin. It takes an annealing temperature of 550°C for the former to become fully coarse grained across the joint while the joint produced with the triangular pin is largely covered with coarse grains starting at 500°C. The higher resistance of the nugget zone obtained with a threaded circular pin to grain coarsening appears to be critical in the selection of the pin profiles when the manufacturing cycle of the welded EN AW 5083 plates involves post-welding heat treatments.     

Microstructure and notched tensile fracture of Ti–6Al–4V to Ti–4.5Al–3V–2Fe–2Mo dissimilar welds

Dissimilar welding of Ti–6Al–4V (Ti-6-4) to Ti–4.5A1–3V–2Fe–2Mo (SP-700) alloys was performed using a CO₂ laser. The microstructure and notched tensile strength (NTS) of the dissimilar welds were investigated in the as-welded and post-weld heat treatment (PWHT) conditions. Moreover, the results were compared with homogeneous laser welds with the same PWHT. The dilution of SP-700 with the Ti-6-4 alloy caused the formation of fine needle-like α + β structures, resulting in the exhibition of a moderately high fusion zone (FZ) hardness of HV 398. The high FZ hardness (HV 438) for the weld with the PWHT at 482 °C was associated with low NTS or high notch brittleness. The fracture appearance of the notched tensile specimen was related to its inherent microstructure. With increasing the PWHT temperature, the thickness of grain boundary α increased, which promoted an intergranular dimple fracture. By contrast, fine shallow dimples were present in the peak-aged weld, which was induced by the refined α + β microstructures in the basket-weave form.     

Joint properties of friction welded joint between pure magnesium and pure aluminium with post-weld heat treatment

The present paper described the investigation of the joint properties of friction welded joint between pure magnesium (CP-Mg) and pure aluminium (CP-Al) with post-weld heat treatment (PWHT). The joint in as-welded condition fractured from the adjacent region of the weld interface, although that had the same strength as the tensile strength of the CP-Al base metal. This joint had the intermediate layer (interlayer) consisting of intermetallic compound (IMC) on the weld interface, and its thickness was below approximately 1 μm. Most of joints subjected to PWHT autogenously fractured at IMC interlayer and that mainly occurred between Mg₂Al₃ and Mg₁₇Al₁₂ although those layers had a little each other at the fractured surfaces. The IMC interlayer grew to CP-Mg and CP-Al sides, and its thickness increased with increasing heating temperature and/or heating time. The main reasons for the autogenous fracture from the adjacent region of the weld interface of the joint were considered the growth of IMC interlayer of the joint during PWHT process. Furthermore, that fracture of the joint was thought the generating of the thermal stresses in the radial and/or circumferential directions during the cooling stage of PWHT process.     

Effect of solution treatment temperature on tensile properties of AI-7Si-O.3Mg (wt-%) alloy

Abstract

The effect of solution treatment temperature on the tensile properties of an AI-7 Si-0.3Mg (wt-%) alloy has been studied using tensile and hardness testing, microprobe composition analysis, and differential scanning calorimetry. With a sufficiently long solution treatment time, an increase in solution treatment temperature from 500 to 560°C significantly increases the silicon content in the matrix, but has little effect on the magnesium content. This results in a slight increase in the peak aged yield strength, but a more significant increase in the peak aged ultimate tensile stress and hardness. The alloy ductility is independent of solution treatment temperature, but is clearly influenced by the degree of eutectic silicon particle spheroidisation and coarsening. Using a higher solution treatment temperature can shorten the solution treatment time required to achieve a given tensile elongation value.     

热输入对Inconel 617镍基高温合金激光焊接接头显微组织与力学性能的影响EI北大核心

采用两种热输入不同的焊接工艺参数对3 mm壁厚的Inconel 617镍基高温合金进行激光焊接。通过光学显微镜和扫描电子显微镜对焊接接头显微组织进行观察分析,并测试了焊接接头在室温(25℃)及高温(900℃)下的拉伸性能。结果表明:激光焊接热输入对Inconel 617焊接接头显微组织及力学性能影响明显。在高热输入(200 J/mm)条件下,焊缝正面宽度3.88 mm,熔化区中部晶粒尺寸粗大,取向杂乱,树枝晶二次枝晶间距较大(6.71μm),枝晶间碳化物颗粒尺寸较为粗大,枝晶间Mo,Cr等合金元素的凝固偏析较为严重。焊接接头热影响区宽度约0.29 mm,在晶界和晶内形成了γ+碳化物共晶组织,这是由于焊接升温过程中,热影响区内球状碳化物颗粒与周边奥氏体发生组分液化,并在焊后凝固过程中形成共晶。低热输入(90 J/mm)工艺参数获得的焊缝正面宽度为2.28 mm,焊缝呈沿熔合线母材外延生长并沿热流方向定向凝固形成的柱状晶形态。焊缝中部树枝晶二次枝晶间距较小(2.26μm),枝晶间碳化物颗粒尺寸细小,热影响区宽度约0.15 mm。室温(25℃)拉伸测试表明:高热输入下获得的焊接接头由于焊缝中固溶元素偏析造成的局部组织弱化,从焊缝中部破坏,强度与伸长率有所降低,低热输入条件下获得的焊接接头从母材破坏。而高温实验条件下(900℃),母材晶界发生弱化导致所有试样均从母材破坏。